This invention relates generally to an improved method for lubrication of metal workpieces being formed at elevated temperatures of at least 250.degree. C. and higher and more particularly to a novel lubricant combination for such method of metal forming which includes formation of an improved polymer lubricant in situ at the elevated working temperatures.
Various lubrication means are known whereby metal workpieces being formed at elevated temperatures with one or more die members, such as by forging or extrusion, are provided with lubrication both prior to and during the metal forming operations. Both workpieces and die members are often heated to very elevated temperatures, particularly if ferrous metals are being formed, with lubricant often being supplied in copious quantities to provide both lubrication and cooling of the die members. For example, U.S. Pat. No. 2,821,016 describes the hot forging of steel billets or slugs preheated at temperatures up to 2300.degree. F. and thereafter formed with movable and fixed die members being maintained with the liquid lubricant below 1000.degree. F. In doing so, the die members are now conventionally flooded with a lubricating solution of colloidal graphite suspended in water containing a soluble oil. While such lubrication is reported to prevent "score" marks on the forged product and die members, it has also been found that considerable cleaning of these articles is required to remove adherent carbon particles.
Other water-based lubricants have similarly been employed which are said to provide a better lubrication means than achieved with "oil-base" suspensions of graphite and still other particulates. For example, there is disclosed in U.S. Pat. No. 4,401,579 a lubricant composition employing fumaric acid salts as the primary lubricating and release agent for use in forging operations. As therein employed, such lubricant compositions can further include other suitable thickeners and polymethacrylates, polyvinyl alcohol, starch, gelatin, gum arabic and polysaccharides along with surfactants, wetting and dispersing agents. Suitable use of such lubrication means is further said to include other metal forming operations such as drawing, press forming, extrusion, wire drawing and other processes where workpiece temperatures reach at least about 800.degree. F. In a reported test the die members were preheated to 500.degree. F. with the die members being sprayed with the disclosed lubricant while low carbon steel billets heated to 2150.degree. F. were being forged therein. A different lubricating composition is disclosed in U.S. Pat. No. 4,765,917 for use in elevated temperature metal forming operations. This water-based lubricant is said to comprise about one percent to about forty percent by weight of a polycarboxylic acid salt reaction product, such as trimellitic acid and an alkyli metal or an alkaline earth metal hydroxide such that the pH of the composition is about 6.5 to about 10 along with about 0.1 percent to about 12 percent by weight of a water dispersable thickening agent, and the balance water. Such water-based lubricant is said to further optionally include extreme pressure additives, performance enhancers and biocidal agents. Representative extreme pressure additives are said to include phosphate esters while listed performance enhancers include ammonium phosphate and alkyl-metal polyphosphates. As therein employed, such lubricant composition is reported suitable in hot forging processes and other metal forming operations such as drawing, press forming, extrusion, wire drawing and like processes where workpiece temperatures generally reach at least about 1100-1300.degree. F. for aluminum pieces and 1300-2300.degree. F. (generally 1800-2000.degree. F.) for steel workpieces. The average die temperatures are reported to be about 600.degree. F. with die temperatures varying from about 250.degree. F. to 900.degree. F. A reported test for hot drawing of steel artillery shell casings supplied such lubricant to the preheated punch or ram members over a time period varying between eight to eleven seconds with said time period said to be less than a twenty second spray period previously required with another prior art lubricant.
In a still pending continuation application Ser. No. 08/381,144 entitled "Elevated Temperature Metal Forming Lubrication Method", filed Jan. 30, 1995 in the name of Edgar Earl Graham and assigned to the present assignee, there is described a novel lubricant combination for such method of metal forming which includes formation of a novel polymer lubricant at the elevated working temperatures. In said method of lubrication, a vaporizable and polymerizable organic reactant selected from the group of phosphate esters and phosphazene compounds is applied to form a solid polymer lubricant in situ upon contacting the forming die with a preheated workpiece. A water-based emulsion containing such organic reactant can be applied directly to the shaping region of the forming die as well as further applied to the preheated metal workpiece in carrying out the disclosed lubrication means. Comparative test results reported in said pending application found superior die lubrication to have been achieved with the disclosed lubrication means to include a five percent reduction in forming pressures when utilizing a commercially available tertiary butylphenyl phenyl phosphate as the polymer forming lubricant.
Still another pending application Ser. No. 08/275,449 entitled "Elevated Temperature Metal Forming Lubrication" filed Jul. 14, 1994 also in the name of Edgar Earl Graham and assigned to the present assignee, discloses further improved lubrication means employing the same class of polymer forming organic reactants in combination with graphite particulates. More particularly, an addition of approximately 0.5 percent by volume graphite particulates in the aqueous emulsion containing the previously employed commercial butylphenyl phenyl phosphate ester enabled significantly lower working pressures to be utilized. Additionally, such combined lubrication means were found to enable considerable more satisfactory workpieces to be formed than was produced with such precursor organic reactant alone at much higher applied pressures. Representative phosphate esters disclosed for use in both of said commonly assigned pending applications include triaryl phosphate esters such as tricresyl phosphate and triphenyl phosphate, mixed cresyl-xylenyl phosphates and cresyl diphenyl phosphates.
It is one object of the present invention, therefore, to provide a still further improved method for lubrication of metal workpieces being formed at elevated temperatures utilizing novel lubrication means.
It is still another object of the present invention to provide improved lubrication means for metal workpieces being formed at elevated temperatures with superior lubricant compositions.
It is a still further object of the present invention to provide a novel method for lubrication of metal workpieces being formed at elevated temperatures which employs relatively low lubricant levels at further reduced working pressures.
These and further objects of the present invention will become apparent upon considering the following detailed description of the present invention.